1. Field of the Invention
The present invention generally relates to electronic devices such as thin film transistors (TFTs) and to flat display devices having the same. More particularly, however, the invention relates to an electronic device and to a flat display device having the same in which electrostatic damage caused by static electricity is prevented or reduced.
2. Description of the Related Art
Many kinds of display devices are used for displaying images. Recently, a variety of flat display devices have replaced cathode ray tube (CRT) displays. Flat display devices may be classified either as emissive or non-emissive depending on the type of light emission used. Emissive display devices include flat CRT display devices, plasma display panel devices, vacuum fluorescent display devices, field emission display devices, and organic/inorganic electro-luminescent display devices, and non-emissive display devices include liquid crystal display devices. Flat emissive organic electro-luminescent display (OELD) devices garner attention since they are emissive and do not include a light emitting device, such as a back light, and are capable of operating with low power consumption and at high efficiency. Advantages of OELD devices include low operating voltage, a light weight, a thin profile, wide viewing angles, and fast video response times.
A conventional electroluminescent unit of an OELD device includes a first electrode (anode), formed in a stack on a substrate, a second electrode (cathode), and an organic, light emitting layer (thin film) interposed between the first and second electrodes. In operation, OELD devices emit light of a specific wavelength using energy generated from excitons formed from recombining electrons originating from the anode and holes originating from the cathode that are injected into the organic thin film. An electron transport layer (ETL) may be interposed between the cathode and the organic emitting layer. Similarly, a hole transport layer (HTL) may be interposed between the anode and the organic emitting layer. Also, a hole injection layer (HIL) may be disposed between the anode and the HTL. Additionally, an electron injection layer (EIL) may be interposed between the cathode and the ETL.
A passive-matrix (PM) organic electro-luminescent display (OELD) device may use a manual driving method, while an active matrix (AM) type may use an active driving method. In the PM OELD device, the anodes are arranged in columns and the cathodes are arranged in rows, respectively. A row driving circuit supplies scanning signals to the cathodes while a column driving circuit supplies data signals to each pixel. On the other hand, the AM OELD device uses a thin film transistor (TFT) to control a signal inputted to a pixel. AM OELD's are widely used for implementing animation because their use of TFT's enables them to process a large number of signals quickly.
A disadvantage associated with conventional AM OELD devices is that one or more faulty pixels may develop in a display region due to generation and/or discharge of static electricity during manufacture or operation of the device.
FIG. 1A is a plan view photograph of a conventional OELD device that shows faulty pixels as bright spots. FIG. 1B is a magnified photograph of a normal pixel indicated as A in FIG. 1A, and FIG. 1C is a magnified photograph of faulty pixel indicated as B in FIG. 1A. FIGS. 1B and 1C are bottom views of the conventional OELD device of FIG. 1A. These bottom views are taken looking through the multilayered structure of the substrate and the various electrical and electroluminescent components formed on it. Thus, in FIGS. 1B and 1C, the gate lines 3a and 3b appear to be positioned above the conductive layer 5.
In FIGS. 1B and 1C, each of the pixels 1a and 1b comprises an electroluminescent unit, a gate electrode (2a in FIG. 1B and 2b in FIG. 1c), and a light emitting thin film transistor (Ma in FIG. 1B and Mb in FIG. 1C) that transmits electrical signals from a driving TFT (not shown) to the pixel. Source electrodes of the light emitting TFTs Ma and Mb are electrically connected to the driving TFTs (not shown) via conductive layers 5.
FIG. 1D is a magnified plan view of a portion indicated as B′ in FIG. 1C. Referring to FIG. 1D, a conductive layer 5 may extend across other conductive layers. In the magnified bottom view of FIG. 1D, for example, the conductive layer 5 is shown crossing the gate line 3a/3b. In this exemplary drawing, the gate line 3a/3b appears to be positioned above the conductive layer 5. In operation, the gate line 3a/3b acts as a scan line and/or an extension unit of a scan line for supplying electrical signals to a thin film transistor.
To meet design specifications, the width of each gate line 3a/3b may change along a length thereof. In the conventional design illustrated in FIGS. 1B, 1C, and 1D, for example, each gate line 3a/3b changes in width at a portion thereof that crosses the conductive layer 5. As shown in FIG. 1D, the wider portion of the gate line 3b may be a width change part Aw, and a narrower connected portion of the gate line 3a/3b may be a crossing unit Ac. Both the width change part Aw and the crossing unit Ac may be insulated from the conductive layer 5 and positioned within the side boundaries thereof. Because electricity tends to discharge at the pointed ends of a conductor, an electrostatic discharge (ESD) tends to occur at an angled portion Ad of the width change part Aw shown in FIG. 1D. In most cases, the ESD damages the corresponding pixel 1a/1b, causing it to overluminate (e.g., appear as a bright spot, such as the bright spot B shown in FIG. 1A). Such an ESD is easily induced since static electricity is concentrated at the crossing portion, and thus, the possibility of generating a short circuit between crossed conductive layers increases if an insulating layer interposed between them is damaged. As depicted in FIGS. 1B and 1C, even though the same electrical signal is inputted to the pixel 1a in FIG. 1B and the pixel 1b in FIG. 1C, the pixel 1b in FIG. 1C malfunctions and produces a bright spot having a greater brightness than the normal pixel in FIG. 1B. The greater brightness occurs because the short circuit between different conductive layers 3b and 5 creates and applies a different electrical signal than one that is desired. This undesired ESD may degrade a flat OELD's picture quality, which requires high uniformity over an entire display region of the OELD.